1. Field of the Invention
The present invention relates to a soft magnetic film being used for a recording magnetic pole of a magnetic head, a thin film inductor, various kinds of thin film sensors and the like and manufacturing method thereof, and a magnetic head using thereof.
2. Description of the Related Art
In recent years, high densification of recording density is strongly demanded in the field of magnetic recording. In response to this demand, a recording bit on a recording medium is made fine. The fine recording bit is likely to be disturbed thermally. Therefore, in order to secure thermal stability of the recording bit, a recording medium of higher coercive force has been used.
To respond to higher coercive force of recording medium side, a magnetic head capable of generating higher recording magnetic field is required. To enhance recording magnetic field of a magnetic head, soft magnetic material of high saturation magnetic flux density is indispensable as material of magnetic pole. Soft magnetic material serving as material of magnetic pole is important to further possess low coercive force and high permeability, soft magnetic material having these magnetic properties at the same time is required.
As soft magnetic materials being employed conventionally for thin film magnetic heads, various materials such as ferrite, Sendust alloy, Co based amorphous alloy and the like have been developed. However, ferrite is such low in its saturation magnetic flux density as less than 10 kG, it is not suitable for high density recording due to higher coercive force of magnetic recording medium. Saturation magnetic flux density of Sendust alloy is higher than ferrite, but is approximately 10 kG, it can not sufficiently respond to higher density recording. Co based amorphous alloy is low in its crystallization temperature, causes accordingly thermal instability in the manufacturing process of a thin film magnetic head, resulting in inability of obtaining high permeability, high specific resistance inherent to amorphous alloy.
In recent years, with an object to attain high densification of saturation magnetic flux, various materials of soft magnetic thin film having Fe as a main component have been proposed. For instance, it is known to obtain soft magnetic properties by making small effective magnetocrystalline anisotropy through micro-crystallization of grains which have Fe as a main component. However, this method requires addition of approximately 10 to 20% of additional elements such as Zr, Nb, Hf, Ti, Ta and N, B, C to obtain thermal stability of micro-crystalline grains, the upper limit of saturation magnetic flux density was about 18 kG. Even if such an alloy film is made soft magnetic, its saturation magnetic flux density does not exceed that of pure Fe (21.5 kG).
In future, it is expected that further higher densification of recording density will be demanded. In such a case, soft magnetic material of still high saturation magnetic flux density is necessary. From such a view-point, Fe--Co alloy of the highest saturation magnetic flux density among alloys is attracting attention. However, Fe--Co alloy, in a composition of saturation magnetic flux density higher than Fe, is known to possess large magnetostriction and magneto-crystalline anisotropy. Therefore, it was very difficult to make it soft magnetic.
Additional element is added to Fe--Co alloy to make micro-crystalline, even if being made soft magnetic thereby, in that case, the additional element is required to be added much. Therefore, high saturation magnetic flux density of the Fe--Co alloy can not be maintained.
On the other hand, a method is proposed in which, through addition of rare earth elements to the Fe--Co alloy to lower its large saturation magnetostriction, excellent soft magnetic properties are obtained (Ref. to Japanese Patent Laid-open Application Numbers Hei-5-39550 and Hei-6-53040). Here, by substituting rare earth element in the Fe--Co alloy to be supersaturated solid solution, a body-centered cubic structure is maintained through a whole film. According to the reason disclosed in that, when the rare earth element is added much, amorphous phase appears to deteriorate the saturation magnetic flux density.
Further, the rare earth elements to be added are restricted to 3 elements of Sm, Ho, Tm. The reason for this is that, when substitution solid solution is prepared with addition of rare earth element, only these 3 elements give lowering effect of magnetostriction. Further, because of single phase of body-centered cubic structure, sufficient microcrystallization is difficult, accordingly coercive force can not be fully reduced to be used for magnetic head and the like.
In addition, there are such difficulties that, since the soft magnetic alloy film in which rare earth element (Sm, Ho, Tm) is supersaturated in substitution solid solution of Fe--Co alloy is thermally unstable, almost of the film tends to be amorphous to cause deterioration of saturation magnetic flux density.
In order to incorporate such an alloy film as a material of a magnetic pole of a magnetic head, the soft magnetic properties such as permeability and coercive force are insufficient and are desired to be further improved.